The present invention relates to a method for synthesis of core-shell type and solid solution alloy type metallic nanoparticles via transmetalation reactions and their applications. More particularly, the present invention relates to a method for synthesis of core-shell type and solid solution alloy type metallic nanoparticles (including rod shape, hereinafter referred to as xe2x80x9cnanoparticlesxe2x80x9d) in which the particles have a size of 1 to 100 nm and comprise two or more metals.
The term nanoparticles denotes particles whose size is from 1 to 100 nm and having characteristic optical, electrical, magnetic and catalytic properties different from the same bulk matter, due to their quantum effect and large surface area. For this reason, currently, there is much effort being made to develop a synthesis method of such nanoparticles. In spite of such efforts, however, the synthesis methods developed up to now are still far from perfect. Metallic alloy nanoparticles may compensate for the defects of single element nanoparticles, such as tendency to be readily oxidized, corrosiveness, and deterioration of chemical-physical properties. Also, they may exhibit enhanced catalytic effects in chemical reactions. In case of using magnetic metals, the resulting nanoparticles may have increased coercive force by increase of magnetic anisotropy. Further, it is possible to use the alloy nanoparticles as materials for magnetic recording media since they are stable in the air to not undergo oxidation.
So far, most alloy structures have been achieved by using a physical vacuum vapor deposition method to form a thin layer. Research and studies on such vacuum vapor deposition method have been conducted. However, the above method has disadvantages such as chaotic growth of particles and non-uniformity of particle size thereby causing deterioration of properties of the particles.
Recently, Sun et al. have developed a novel synthesis method for forming a thin layer of nanoparticles with improved properties (see, Science-2000, 287, 1989).
As methods using chemical synthesis methods, it has been reported that cobalt-platinum and iron-platinum alloy nanoparticles are prepared by reducing metallic ions or organometallic compounds to metals using chemical reducing agents such as hydrides for example, NaBH4, NaBEt3H, and N2H4 (see, for example, Science. 2000, 287, 1989; J. Appl. Phys. 2000, 87, 5615; J. Phys. Chem. B 2000, 104, 695; and J. Appl. Phys. 1999, 85, 5184). Also, Sun et al. at IBM have tried to apply cobalt nanoparticles produced via chemical reduction with a hydride or diol to single electron devices.
Similarly, with respect to gold-silver, copper-silver, copper-palladium, palladium-platinum, palladium-gold and copper-platinum alloy nanoparticles, production methods by reduction using hydride or alcohol as a reducing agent also have been described (see, for example, J. Phys. Chem. 1992, 96, 9730; J. Phys. Chem. 1997, 101, 5301; J. Phys. Chem. 1991, 96, 7448; Langmuir, 1995, 11, 693; Chem. Mater. 1993, 5, 254; Chem. Mater. 1996, 8, 1895; Langmuir, 1994, 10, 4574; Langmuir 1993, 9, 1664; J. Phys. Chem. 1992, 96, 9927; and J. Phys. Chem. B 1997, 101, 7033).
Such noble metallic nanoparticles can be used as reducing catalysts in the reduction of double bonds in organic compounds such as olefin. This is because the reduction in size of particles to nanometer level leads to an increase of surface area and thereby, activity level.
As discussed above, there have been made numerous efforts to find, a method for synthesizing nanoparticles consisting of heterogeneous elements. However, it is not secured that nanoparticles produced by the method described in the above-listed studies have a uniform particle size, and composition ratio of the nanoparticles cannot be stably controlled. Therefore, there are problems in their utility for actual industries, as well as in preparing core-shell type nanoparticles themselves.
The present inventors have studied to overcome the several problems occurring in the prior art and to develop a novel method for synthesizing core-shell type and solid solution alloy type metallic nanoparticles. As a result, they have accomplished a novel method for synthesizing core-shell type and solid solution alloy type metallic nanoparticles by only a metallic transmetalation reaction taking advantage of oxidation-reduction potential differences between heterogeneous metals, without any additional catalyst. This forms the present invention.
The transmetalation reaction between two metals according to the present invention occurs due to the redox potential difference between them. That is, because of the potential difference between two metals, when they come into contact with each other, one metal atom of 0 charge is oxidized to form an ion and the other ionic metal is reduced to form elemental metal, whereby transmetalation reaction between two metals occurs. Reactivity of such substitution reaction can be predicted in accordance with the ionization tendencies of the reactant metals.
Therefore, the object of the present invention is to provide a method for producing core-shell type metallic nanoparticles having a stable and uniform particle size, or solid solution alloy type metallic nanoparticles having a certain composition ratio, via transmetalation reactions of various metals without any additional reducing agent, on the basis of the ionization tendencies of the substituent metals.
Another object of the present invention is to provide applications in various industrial fields, including information recording media, catalysts, medical treatment agents, etc., using the metallic alloy nanoparticles produced according to the present invention.
Thus, in the first aspect of the present invention, there is provided a method for producing core-shell type metallic nanoparticles comprising (i) providing a dispersion of a first metal as nanoparticles in an appropriate organic solvent; (ii) providing a solution of a metallic precursor containing a second metal in an appropriate organic solvent, in which the second metal has a reduction potential higher than that of the first metal; and (iii) combining the dispersion from (i) and the solution from (ii) together to carry out the transmetalation reaction of the first and second metals, thereby forming core-shell type metallic nanoparticles.
In the second aspect according to the present invention, there is provided a method for producing solid solution alloy type metallic nanoparticles comprising (i) providing a solution of a thermally degradable metallic precursor containing a first metal in an appropriate organic solvent; (ii) providing a solution of a metallic precursor containing a second metal in an appropriate organic solvent, in which the second metal has a reduction potential higher than that of the first metal; and (iii) combining the solutions from (i) and (ii) together to carry out the transmetalation reaction of the first and second metals, thereby forming solid solution alloy type metallic nanoparticles